There are two potential pathways for the movement of auxin between plant cells: cellular and symplastic. In the cellular pathway, auxin passes through the cytoplasm of individual cells and across cell membranes. In the symplastic pathway, auxin moves directly between cells through cytoplasmic connections called plasmodesmata. Evidence suggests plasmodesmata may serve as channels allowing passive movement of molecules like auxin between cells. Polar transport of auxin is significant as it relates to the morphological polarity of plants and could control growth and differentiation. While polar transport manifests physiological polarity, the embryo's morphological polarity precedes and seems to cause the development of polar transport.

1. PREPARED BY NGUMBA,NEHEMIA JONAS
SOKOINE UNIVERSITYOF AGRICULTURE,MOROGORO TANZANIA
MAZIMBUCAMPUS2016,DECEMBER,2016
CELLULAR VERSUSSYMPLASTIC PATH OF MOVEMENT
There istwo differentpathsof movementinthe sectioncanbe visualized,inthe firstsectionthe auxin
wouldpassthroughthe cell of the sectionandmove throughthe cytoplasmandthenpassacross the
cell membrane intothe extracellularspace before enteringinthe nextcell while inthe secondphase the
auxinwouldsimplyenterinthe cytoplasmof the firstcell andmigrate tothe nextcellsviathe
cytoplasmicconnectionsof symplastandbecomingextracellularonlyasitleavesthe basal cell toenter
the receiver.The plasmodesmatahave beentakenintoconsiderationas likelychannels fortransport
and communicationbetweencells. A new approachusedto determinewhetherthe plamodesmaare
pathwaysfortransport issuggested bythe discoveryof connectionsof low electrical resistance between
certainanimal cells.If the plasmodesmaof higherplantcellscanbe showntopasselectriccurrents
whichare indicativeof passive movementsof ionsbetweencellsthiswouldenhancelikelihoodthatthey
may alsoserve aschannelsforthe movementof auxinandothermolecules.( Willkins,1969, PP.131).
SIGNIFICANCEOFPOLAR TRANSPORT
The significance of polartransporthasarouse interestnotonlybecause of the processis intrinsically
interestingbutalso itmightrelate tothe morphological polarityof plantsandthiscouldbe a controlling
factor ingrowthand differentiationdue tothisevidence itshowsthatif the polartransportiscausally
relatedtomorphological polarityitshouldoccursindevelopingembryosandbe presentfromthe time
of germination.The mostimportantpointisthatthe morphological polarityof the embryoandthe
seedlingproceed the developmentof polartransportthusthe polartransport itseemto be a
physiological manifestationof the inherentlongitudinal polarityof the plantthana cause of this
polarity. The elegantinvestigationsonthe control of vasculardifferentiationincoleusare one of the
mostcomplete descriptionsavailable of the interactionbetweenauxintransportand differentiationand
hence the auxinslimitsthe regenerationof bothxylemtracheidandphloemsievetubesarounda
woundseveringavascularstrandinthe stem.Whendifferent numberof youngleavesabove asevered
vascularstrand is removedthe numberof xylemstrandsthatregenerateisproportionaltothe amount
of auxinproducedbythe remainingleaves.Furthermore the reductioninxylemregenerationwhenall
the leavesabove the woundare removedcanbe completelyovercomeif the amountof auxinthey
supplyisreplacedbysupplyisreplacedbyapplyingIAA. .( Willkins,1969, PP.131).